Amplifying system for television



Sept. 22, 1936. T. NAKASHIMA ET AL 2,055,156

AMPLIFYING SYSTEM FOR TELEVISION I Filed Nov. 8, 1932 2 Shets-Sheet IF'. EMU:

I m I IILI M-I LPI-IJH Kfl i ro Takal gnag p 1936- T. NAKASHIMA ET AL2,055,156

AMP-LIFYING SYSTEM FOR TELEVISION Fild NOV. 8, 1932 2 Sheets-Sheet 2Patented Sept. 22, 1936 AMPLI YING PATENT OFFICE Tomomasa Nakashima. andKenjirc-Takayanagi,

Hama'matsu-shi, Japan,

. Application November 8, 1932, Serial no. 641,706 In Japan January 2,1932 54 Claims. 179-471) Our invention relates toiinpiovements inamplifying systems and more particularly to improvements in systems foramplifying photoelectric current in televisiontransmitting systeins. i a

One object of our invention is to provide means for amplifying imagecurrent or photo-electric current in television transmitting systems atsubstantially a constant degree throughout the wide frequency range fromabout ten cycles to several over, per second Another object of ourinvention is to provide. amplifying apparatus with extremely lowdistributed static capacity.

A further object of our invention. isto provide means for compensatingfor-'image-current deviation at the upper or high-frequency region ofthe frequency range. I

A further object of ourinvention is to provide means for compensatingfor the lowering amplification characteristic at the upperregionflof thefrequency range. r

A still further object of our invention is to provide a system foramplifying a current whose frequency varies from about ten cycles toseveral hundred thousand cycles per second at substantially 'a constantdegree of amplification.

Other objects and features. of our invention will be apparent from theappended claims and the following description in connection with theaccompanying drawings, wherein:

Fig. 1 shows the usual capacity-coupled resistance amplifier system forradio telephonyv Fig. 2 shows an equivalent circuit of one stage of thesystem shown in Fig, .1. i r

Fig. 3 is a diagrammatic illustration of one embodiment of ourinvention.

Fig. 4 shows an equivalen'tcircuit of one stage of the system shown inFig. 3.

Fig. 5 shows diagrammatically, partly in section, a preferredconstruction and arrangement of an amplifying apparatus according to ourinvention provided with means for minimizing the distributed capacity.

Figs. 6 and "7 are curves showing amplification characteristics andphase characteristics, respectively, of our improved system.

In the system for televising moving pictures or other movingobjects, itis desirable tofu'se a large number of view-elements, or picture-elements, say ten thousand or above, in order to secure a clearreproduction oftelevised' views, and if such a large number ofview-elements are used, the modulating current Variation takes place ata rate corresponding to a frequency which varies from about ten cycles.to several hundred thousand cyclesper second according to the rate ofchange of the darkness of suc-' cessive view-elements swept by ascanninglightm; i

Referring to Fig. "1, the system shown comprises a triode amplifier"tube I whose grid circuit is connected to a source of current to beamplified, .not shown, and the plate circuit of which is coupled to thegrid circuit of a similar amplifier tube 2 of the succeeding stage,through a coupling condenser '3. The plate circuit of the tube 2 iscoupled to a succeeding amplifieror a modulator, not shown, in the usualmanner.

The plate circuit of the amplifier tube 1 in:- cludes a couplingresistance 4 in series, and the potential difference across theresistance is applied to the, gridelectrode of the second tube 2.

As far as the frequency range under considertion is concerned, anequivalent circuit for the tube I and its associated parts may be drawnas shown in Fig. 2, wherein5 representsthe internal resistance of thetube I, and 6 the static capacity of thetube 1 together. with .wiringstherefor. I shows the grid resistance and 8 the eifective staticcapacity of tube'land itswiring. According to our invention, in order toobtain an adequately constant degree of amplification at the lowfrequency region of the; frequency range, including 10 cyclesper'second, the re actance due to the coupling condenser 3 at such lowfrequency should be negligible in comparison with thegrid resistance 1.For example, if the condenser 3 has a capacity of 0.1 microfarad, theresistance 1 should beimore than 1.5 megohms.

On the other hand, in order to obtain constant amplificationcharacteristic at the upper region of the frequency range, includingseveral hundred thousand cycles per second, the resistance 4 should benegligible in comparison with the reactance due to the capacities G and,8 atsuch high frequency. However, the reductionin the value ofresistance 4 causes a reduction in the degree of amplification, and inorder to obtain as high as" possible a degree of amplification, it isproposed to reduce the capacities 6 and 8, thus permitting theme of-a*'rel ativel'y high resistance 4. A preferred construction suitablefor such reduction in the capacities is shown in Fig. 5, and

will be described hereinafter. l

With the above arrangement, we obtain a substantially constant degree ofamplification throughout the whole frequency range from about ten toseveral hundred thousand'cycles I coil in series with'ithe resistance 4.r

' includes a repeating resistance corresponding Referring to Fig. 3,tetrode tubes 2| and 22 are utilized as amplifiers. While we show onlytwo such tubes, it will be understood that this is merely'by way ofexample and there is no limitation as to the number of amplifier tubesutilized. Tetrode tubes have no feed-back action, and have a relativelyhigh coeflicient of amplification. The plate I circuit of each tube toresistance 4 of Figure 1 and a self-inductance coil 29, respectively,and the succeeding two stages are coupled with each other throughv acoupling condenser 23. The grid circuit of each tube includes e.gridQresistance 21 corresponding to lof Figurel.

fAs-far. asth'e upper portion of the frequency range'in questionis'concerned, an equivalent circuitmay be drawn as shown in Fig. 4, inwhich represents, the internal resistance of the first amplifiertube 2|,and 28 the static capacity of the whole circuit, the capacity ,28corresponding to the sum of the capacities, 6' and 8 of Fig. 2. Theinductance coil 29 has distributed capacity v3! and resistance 32 whichrepresents allthe energy losses, within the coil 29 As will readily beunderstood, the self-inductance 29 affects the whole circuit inv thereverse sense to the capacity 28. I

' Assuming that R represents the resistance value of the resistor 24, Lothe self-inductance of the coil '29, Co'the capacity 3|, C the capacity28, we the angular velocity of the natural frequency of the coil 29,.andw the angular velocity of the frequency of amplified current, andalso that the resistance 321isjinfinite or there is no'energy losswithin the 'icoil 29, as is permissible for the frequency. range underquestion, the imaginary component'of the resultant impedance Z of thecircuitbetween the two points a and b shown in Figniis '.i r tiifflc)]*1, w) 1) For any'ffrequency'of amplified current within thefrequency range under question, the ratio w/ o may be equalto or smallerthan 0.4, and

additional capacitance in parallel with thecoil 29, and

t-eri een For the purpose of the present invention to prevent any phasedisplacement of amplified current, the imaginary component 7X should bepref- 'erably zero, and we obtain a condition as follows:--

co 2 w 2 wL [12 ]=wCR [12(--) .'.L =CR (4) .may be a slight energy losswithin the coil 29,

without departing from the spirit of the invention.

If K is a factor representing the deviation,

. when C/C'0=0.5, K=0.89

when C/Co=1, K=1 when C/Co=2, K=1.11 when C'/Co=3, K=1.88 when C/Co=4=,K=3.40

L0 is, therefore, as nearly equal to CR (Lo=CR as C/Cc differs from 0.5to 2, provided that an error of about is permissible. For the purpose ofapplicant's invention C. is nearly equal to Co when C/Co is from 0.5 to'2. In Figs. 6 and '7 curves a and b show that the deviation ofamplificationand the phase displacement is negligible for thefrequencies below about 0.6 mega-cycles with C'/Co=2.

In Fig. 6 the ordinate is scaled in transmission units, takingamplification degree at 1000 cycles as unity. Asis well known, fromabout five hundred to several thousand cycles, i. e., at a frequencywhich is so low that static capacities of amplifier tubes, etc., have noeffect, but is so high that coupling capacity and grid resistance haveno effect, the amplification degree is constant. Thisconstantamplification degree A0 is taken as a standard, and if A is theamplification degree at any high frequency, A/Ao shows the percentagevariation of amplification degree from the standard A0 for varyingfrequencies." Such an expression' of relative amplification is a commonprac-v tice (see Experimental Television Transmitting Apparatus by R. D.Kell, Proceedings of the Institute of Radio Engineering, Dec. 1933, vol.21, No. 12, p. 1688).

It is also a common practice to show amplification degree in decibelsNdb,

db 2o g1u fi where V1 is the input voltage and V2 is the output voltageof an amplifier. (See Transmission Networks and Wave Filters, by T. E.Shea, p. 47.) We use decibels 520 m xi) as the'scale of the ordinatein-Fig. 6 instead of For the standard amplification degree A0, the zeroline is utilized and the deviation can be shown by positive or negativevalue depending whether the deviation is above or below. the standard.

In a practical design of our improved system, UY-.224 tubes are used foramplifiers 2| and 22 and the capacity C will be about 20micro-microfarads. The amplification-factor and phase-displacementcharacteristics are shown in Figs. 6 and 7, respectively.

If the Equation (4) is satisfied for the UY-,-224 tubes, L becomes0.18'millihenry. When we use a sent a resistor with a ar" ma ter are};self-made; tance coil with- 110, of 0.2 inillihen'ry having dise tributed capacity of 1'0 miemgmi'crer aus, jea

pacity Cybeing 20' mierc-nnero-rara sw'ejobtain characteristic cui'vesdjandf b 1 Figs. canes, respectively in 'whichithe. Equation 4 isapproxie; mated. a Q

Our invention iiirther includes a compensator for the .dropand thephaseIdisplacementof the output voltage orphoto-enetnc current,,whichare inevitable at high reque t-rescue to static capacity ofphoto-electric-cellcircuit, tois'can hing operation where the" scanning.light-beam has an appreciable cross-sectiohal'area, audio Qur.compensator has generally a hohstr liction similar to oura'mplifier,exemplified in Fig. '3 'but it must be so designed J01" adjusted that,theundesirable e-ffect's. "of the] abovefrnentioned static capacitiesand scanning operation, are'neutrali ized, in other words, thecompensator should have over-compensation characteristics at high fre:

'quehcies, as compared to' thec ase whenit is used as a pure amplifien;For this purpose, the; resistance R must be further "lowered, saytolOOOohms, and, at the same time, the inductance L must also be furtherlowered, e. 'g., to.,0.1 millihenry. By such a reduction theresistancevalue, it may happen that the absolute amplification is necessarilyreduced and consequently material amplification is not effectedat lowerfrequencies, but material amplification i'sobtained atleast at higherfrequencies due to theraisiiig characterist'ioof amplification whichiscaus'ed .by theincrease in the efi'ectfo'i inductance he at highfrequencies, The curves and dinFigs'. hand 7, respectively, show. the'over'-comp'ensation char acteristics of our compensator asabove-specified, and these characteristic curves c and d havesetstanti'al ly similar shapes but o posaesense to the correspondingcharacteristic curves, net; shown but similar to e and respectively, ofthe drop and the phase-displacement f the outputvoltage of photo-cellcurrent,"dueto static. capacity of photo-electric-cell circuit, toscanning operation where the scanning light-beam has-gah appreciablecross-sectional area; and to static capacity of modulator tubes, et'cl,and it will now be obvious that the drop and the phase displacement areadequately compensated for by the compensator according to ourinvention.

In Fig. is shown a preferred construction and arrangement of ourimproved amplifying apparatus in which distributed capacity is reducedto a minimum. The apparatus comprises a cabinet 4! of insulatingmaterial, and having a partition 42 therein forming two compartments orenclosures 43 and 44. Each compartment is shielded by metallic platessuch as copper plate 45 forming a static and magnetic shield.

Within the upper compartment 43 is provided a shelf 46 of insulatingmaterial at the centre portion of the compartment and secured to andsupported from one wall 41 of the cabinet. The shelf carries thereon theamplifier tube 2!, repeating resistance 24, self-inductance coil 29,coupling condenser 23, and grid resistance 21 for the next amplifiertube 22.

The tube 2! extends laterally from the shelf 46 into the uppercompartment of the preceding cabinet 4 I for the preceding amplificationstage,

through openings 48 and 49 provided inthe corresponding side walls ofthe cabinets, and substantially half the length of the tube 2! lieswithin each of the cabinets 4| and 4 l .The tube .22 andits associatedparts are similarly arranged in the next cabinet4l". Wires 51 52", and53, respectively from the coil 29, the "s'creen grid terminal 54 of thetube 2!, and the resistance 27, extend downward, through insulatingbushings 55 mounted inthe partition 42, into the lower compartment .44.Within the compartment 44'are disposed a screengrid bypass condenser 55,a screen grid resistance 51., a plate bypasscon-denser 5B, and a gridbias battery 59. The condensers56 and 58; and the battery 59" areconnected between the respective wires 52, 5| and 53, and the groundedlining 45 of the lower compartment t4, while the wires 52 and 5| extendthrough insulating bushings 60in the bottom wall of the cabinet and arerespectively connected, to energizing sources outside the'cabinet. j

The filament terminals, not shown in Fig 5, are connected to theenergizing source outside thecabihet by means of wires, not shown, whichextend through the back wall 41 of the cabinet. The coupling condenser23 is connected between the plate terminal 6| of the tube 2| and thecontrol grid terminal 62 of the succeeding tube 22, by wires 63. I

Since the parts 23, 24, 21 and 29 are centrally disposed with respect tothe grounded lining 45 of' the upper compartment 43, and since theconnecting wires 5l, 52,.,53 and 63 are of minimum length by properarrangement of the parts, the distributed capacity of the parts andwiring is obviously minimized. V

The capacity is the elementat the high frequency end, that causes thedrop in amplification; Assuming that the amplification resistance isconstant, and that an inductance is put in to balance the capacity, therelative rate of amplification will necessarily be reduced when theinductaneeis. reduced. However, if the amplification resistance; isreduced to one .third, the

lower limit of high frequency, at which thejcaresistance. In Fig. 6, thejc'urve fc is shown with? i'ii the frequency range in which the capacitydoes not substantially aiTect the amplification by the above reasons;

Thus, within the frequency range corresponding to Fig. 6, the relativerate of amplification can be determined by the relative amount of theinductance and resistance.

It must also be noted that, the efiect of inductance at any highfrequency becomes about three times conspicous when the resistance isreduced to one third, and consequently, the relative rate ofamplification is not necessarily reduced by anyreduction in inductanceonly. The curve 0 represents the case when the amplification isdetermined by the relative amount of resistance and inductance and showsthe rais ing characteristic due to the efiect of inductance.

While we have described particular means for practising our invention,it will be recognized that this is only by way of illustration of,general principles and .that our invention is not limited to thatparticular means, but various the anode of said one of the vacuum tubesand the grid of the other of said vacuum tubes, of means, for reducingthe capacity ofsaid tubes and connections, thereof to such a low value Ithat the resistance of said resistor is negligible in comparison to thereactance of said capacity at the high frequencies corresponding to saidnumber of view elements, and a self-inductance coil connected in seriescircuit relation with said resistor, whose self-inductance L is nearlyequal to CR where C is the capacity of the whole circuit and R theresistance of said resistor.

2. man amplificationsystem for television in which the number of viewelements is more than five thousand, the combination with two vacuumtubes, each having an anode, a cathode, a grid and a grid shield, aresistor connected between said anode and said cathode of one of saidtubes, and a condenser connected between the anode of said one of thevacuum tubes and the grid of theother of said vacuum tubes, of aself-inductance coil connected in series circuit relation with saidresistor, the ratio of the angular velocity of the frequency of thecurrent amplified by said system to that of the natural frequency ofsaid self-inductance 0011 being less than 0.4 and the capacity existingalong said coil being nearly equal to the capacity'C of the wholecircuit at the high frequencies corresponding to said number'ofviewrelements, andthe selfinductance of said coil being nearly equal toCR 7 where R is the resistance of said resistor.

due to said scanning operation and static capacity, comprising twovacuum tubes, each having an anode, a cathode, a grid and a grid shield,a. resistor connected between said anode and said cathode of one of saidtubes, and a condenser connected between the anode of said one of vacuumtubes and the grid of the other of said vacuum tubes, means for reducingthe capacity of said tubes and connections thereof to such a low valuethat the resistance of said resistor is negligible in comparison to thereactance of said capacity at the high frequencies corresponding to saidnumber of view elements, and a selfinductance coil connected in seriescircuit relation with said resistor, whose self-inductance L0 is largerthan CR where C is the capacity of the whole circuit and R theresistance of said resistor, Lo and R being respectively of such lowvalue that said drop and phase displacement are compensated for.

4. In a television system in which the number of view-elements is morethan five thousand, and in which the scanning operation is effected byuse of a light-beam having an appreciable crosssectional area, andappreciable static capacity is inevitable due to photo-electric-cellcircuit, modulator tubes etc., a compensator for the drop and the phasedisplacement of the output voltage of photo-electriccurrent at highfrequencies due to said scanning operation and static capacity,comprising two vacuum tubes, each having an anode, a cathode, a grid anda grid shield, a resistor connected between said anode and said cathodeof one of said tubes, and a condenser connected between the anode ofsaid one of vacuum tubes and the grid of the other of said vacuum tubes,and a self-inductance coil connected in series circuit relation withsaid resistor, the ratio of the angular velocity of the frequency of thephoto-electric current to that of the natural frequency of saidself-inductance coil being less than 0.4 and the capacity existing alongsaid coil being nearly equal to the capacity C of the whole circuit atthe high frequencies corresponding to said number of view elements, theself inductance L0 of said coil being larger than CR where R is theresistance of said resistor, and L0 and B being respectively of such lowvalue that said drop and phase displacement are compensated for.

TOMOMASA NAKASHIMA. KENJIRO TAKAYANAGI.

